Operation request: Add PGP Sign

[engrach]

Summary

The PGP operations in CyberChef currently have "Encrypt" and "Encrypt & Sign". There's no only Sign operation.
Please add a PGP Sign operation which only needs the PGP Private key and Private key passphrase.

This allows to only sign and not encrypt a file.

[ordinary-hacker]

ok, sounds nice to add

[engrach]

Looked into the code. This code be a pretty straight forward clone of src/core/operations/PGPEncryptAndSign.mjs. With just some minor modifications.

Simply leave out the encrypt_for parameter in the kbpgp.box request. Also the request for a public key as input can be removed.

[engrach]

See kbpgp documentation
https://keybase.io/kbpgp/docs/encrypting